1. Field of the Invention
The present invention relates to a network apparatus of a large-scale computer system configured such that a plurality of basic elements each having the capacity to operate as one computer are connected by a complete crossbar system.
2. Description of the Related Art
Due to its superior performance, a complete crossbar scheme is generally the most preferred scheme for interconnecting a plurality of basic elements so as not to cause data contention. A complete crossbar scheme means a communication system design in which each distinct pair of basic elements in communication with each other are connected through a different data-communication path; and a way of connection that realizes the complete crossbar scheme using devices having the capability to switch paths is referred to as complete crossbar connection.
One example of the prior art for realizing complete crossbar connection is a network that connects a plurality of basic elements using a single-stage crossbar system (provided as LSI) that realizes complete crossbar connection. Such a network has the advantages of good performance and easy control. Complete crossbar connection using a single-stage crossbar system is next described with reference to FIGS. 1 and 2.
FIG. 1 shows a prior-art example of a network in which complete crossbar connection is realized using one single-stage crossbar apparatus. This network is referred to hereinbelow as the first prior-art network.
As shown in FIG. 1, the first prior-art network is made up of basic elements (100-0)–(100-n) and single-stage crossbar apparatus 200 bidirectionally connected to each basic element. This network of the prior art realizes complete crossbar connection through the use of a single single-stage crossbar device having a switching function for connecting the basic elements.
However, the complete crossbar connection realized in this first prior-art network may entail long distances from the single-stage crossbar apparatus to newly added basic elements as the number of basic elements connected to the network increases. Such a case results in longer cables, and this gives rise to the problem of cable length limitations, such as the problem that normal communication becomes impossible depending on the transmission rate and the problem of the difficulty of maintaining cables as well as the problem of the high expense of the cables, as their length increases.
In addition, in complete crossbar connection as realized by the first prior-art network, an increase in the number of basic elements to be connected necessitates an increase in the number of LSI gates and ports required for switching functions, thus giving rise to the problem of package limitations, such as the problem that the number of required connections exceeds the hardware limits of the single-stage crossbar device itself, and the single-stage crossbar device can no longer accommodate to the problem.
A connection method using a plurality of single-stage crossbar devices has been adopted to overcome the above-described package limitations. FIG. 2 shows an example of a network in which complete crossbar connection is realized using a plurality of single-stage crossbar devices. This prior-art example is hereinbelow referred to as the second prior-art network.
As shown in FIG. 2, the second prior-art network is made up of basic elements (100-0)–(100-n) and single-stage crossbar devices (200-0)–(200-m) bidirectionally connected to each basic element. In this prior-art network, the width of data is divided and assigned to each individual single-stage crossbar device, thereby reducing the data width to be processed by one single-stage crossbar device to limit the number of gates and ports required for each single-stage crossbar device, thereby enabling a solution to the above-described problem regarding package limitations.
With further increases in the number of connected basic elements, however, the complete crossbar connection that is realized in the second prior-art network still necessitates single-stage crossbar devices having a number of ports depending on the number of connections and requires that data width must be further divided. In such cases, the problem arises that, in addition to the previously described package limitations, data cannot be divided beyond a minimum unit of division, i.e., there is a limit to the division of data width.
In the case of a so-called centralized crossbar method in which a plurality of basic elements are connected to one network apparatus as in the above-described first and second prior-art networks, isolating the point of a breakdown is problematic when a breakdown occurs at some point in the network nodes, and this results in the problem that the effect of a breakdown is likely to have repercussions throughout the interconnected network system. There is also the problem that the functions of the entire interconnected network system must be halted when exchanging a failed device inside the device at a particular point in the network nodes.
As a countermeasure for this problem, multi-stage complete crossbar connection has been adopted instead of a single-stage complete crossbar connection, whereby, when a breakdown occurs at a particular point, the effect of the breakdown has been avoided by using a substitute path. As an example of the prior art for realizing multi-stage complete crossbar connection, a third prior-art network that uses a complete crossbar LSI will next be described with reference to FIG. 3.
As shown in FIG. 3, the third prior-art network is made up of: basic elements (100-0)–(100-n); first-layer complete crossbar LSI (300-0)–(300-j) connected to each basic element; and intermediate layer complete cross-bar LSI (400-0)–(400-j) connected to each first-layer complete crossbar LSI.
This network can be configured as a network of a large scale, as a whole, having a complete crossbar-connection configuration by stacking comparatively small-scale complete crossbar units in a plurality of layers, and moreover, enables avoidance of a breakdown at a particular location through the use of a plurality of paths.
However, complete crossbar connection realized by the third prior-art network entails an increase in the number of complete crossbar units in each layer with increases in the number of basic elements to be connected to the network. This increase in complete crossbar units results in an increase in the length of cables connecting the complete crossbar devices in each layer and gives rise to the problem of the cable length limitations.
Furthermore, since the multistage complete crossbar connection in the third prior-art network provides a plurality of paths connecting each of the basic elements, it necessitates a means for effectively controlling the use of the plurality of paths to accommodate increases in the number of basic elements as well as the number of complete crossbar units.
To cope with this problem, a routing control circuit for controlling the employed paths is provided within a complete crossbar unit. There is the problem, however, that the control circuit becomes complex with the increase in the number of paths accompanied by an increase in the scale of the network.
The present invention has been made in view of the above-described problems of the prior art. It is an object of the present invention to provide a network apparatus that keeps cable length unchanged despite increase in the number of connected basic elements and that allows the construction of a network of any scale while keeping the devices for interconnecting basic elements both small-scale and simple.
It is another object of the present invention to provide a network apparatus capable of constructing a network that, in the event of a breakdown at a particular point of a network node, simplifies the setting of a substitute path without affecting the overall network.